The invention is particularly suited to tripod constant velocity joints used for motor vehicle transmission systems.
Such a tripod constant velocity joint generally comprises a male element with ternary symmetry, or tripod, which is integral with a first rotatory shaft, and a female element with ternary symmetry, or tulip, which is integral with a second rotatory shaft.
U.S. Pat. No. 5,330,389 describes a joint comprising a male element that has three arms, one of which is fitted with an outer roller. The arms have a spherical outer surface. Each of the rollers is joined to the arm via an inner ring and a needle crown wheel interposed between the inner ring and the roller. The male element is inserted into a female element provided with rolling tracks and bearings.
In order to prevent jamming of the outer roller in the rolling track during operation, U.S. Pat. No. 5,330,389 on the one hand proposes ensuring that there is sufficient play between the roller and the track, on the opposite side to the driving side. On the other hand, it proposes making the rolling surface of the roller cylindrical, the tracks then having domed surfaces, or giving the tracks planar surfaces and making the rolling surface of the roller domed.
Viewed in section, the bearing areas of the female element and the front surface of the outer roller are inclined with respect to the radial longitudinal plane of the female element. By virtue of this inclination, as the joint is operating the roller's front surface is only applied to the bearing surface that is situated on the contact side between the track and the roller.
During such operation under torque load and at a fracture angle, each outer roller rolling surface is resting on one track of the corresponding pair of tracks, and there is a small amount of play between said rolling surface and the other track of said pair.
Moreover, each arm is in alternating translational motion with respect to the corresponding pair of tracks, parallel to the corresponding radial longitudinal plane. This alternating motion in the radial longitudinal plane is due on the one hand to the arm's inclination and, on the other hand, to the orbital motion, known as offset, of the tripod at triple the frequency of the speed of rotation, something which is well-known in the industry.
Such an alternating motion of the arms induces, in respect of each outer roller, an alternating rocking motion of the roller about the part of its rolling surface that is resting on one of the tracks. The rocking motion is caused on the one hand by the friction created between the spherical bearing area of the arm and the corresponding inner ring, and, on the other hand, by the displacement of the point of contact between the arm's bearing area and the corresponding inner ring.
Accordingly, in respect of each arm, the part of the roller's rolling surface that is diametrically opposed to the supporting one will oscillate.
Such an oscillating motion gives rise to frictional and possibly also jamming phenomena between the roller and the track that is not supporting it.